1. Field of the Invention
The present invention relates to a remote center compliance system used for an assembling apparatus such as a robot, and more particularly, to a remote center compliance system having a variable center which enables various assembly processes without a change of an assembly apparatus by manually or automatically changing the compliance center disposed at the center axis of the assembly apparatus.
2. Description of the Related Art
In general, a remote center compliance system (hereinafter referred to as RCC) enables precision assembly of a circular shaft or pin by correcting a relative positional or angular error between assembled parts generated when an assembly apparatus such as a robot performs various assembly work. The RCC system prevents an assembly apparatus such as a robot from receiving an excessive force so that damage which may occur during an assembly process can be prevented. Thus, the RCC system can improve productivity in manufacturing products.
A conventional RCC system has been disclosed in U.S. Pat. No. 4,098,001. Referring to FIG. 1, the conventional RCC system includes a lower plate 10 connecting a part A to be assembled, an upper plate 20 fixed to an assembly apparatus 1 such as a robot, and a plurality of elastic bodies 30 installed between the upper and lower plates 20 and 10. The system has a special center, i.e., a compliance center Z, disposed at a position spaced a predetermined distance P from a center axis in a coordinate set at the center of the system. When a force is applied in a horizontal direction, the compliance center Z moves only in the horizontal direction without an angular change. Also, when a rotational moment is applied, the compliance center Z rotates only in a direction of the moment without movement in the horizontal direction.
Assuming that the compliance center Z is located at the end portion of the part A fixed to the lower plate 10 of the RCC system, as shown in FIG. 1, when a positional error in the horizontal direction occurs during a process in which the part A is inserted into a hole 5 of a work piece 3, a force in the horizontal direction applies to the compliance center Z due to reaction R at a contact surface. Thus, the part A fixed to the lower plate 10 of the RCC system moves in the horizontal direction and can be inserted into the hole 5, as shown in FIG. 2, so that the assembly process can be smoothly performed at a desired assembly position.
A typical RCC system, however, has a simple structure in which the position of the compliance center Z is fixed. Thus, when parts having various lengths are to be assembled, not only various RCC systems should be used but also the length of a part to be assembly is restricted. That is, when parts having different lengths are to be assembled, an RCC system suitable for the length of each part should be used. Accordingly, replacement of the RCC system during the assembly process is needed.
Consequently, when parts having different lengths are assembled, various RCC systems having compliance centers at difference positions and new equipment replacement of RCC systems of an assembly apparatus such as a robot are required.
To solve the above problems, it is an object of the present invention to provide a remote center compliance system having a variable center by which the position of compliance center enables replacement of an elastic body of an RCC system.
Accordingly, to achieve the above object, there is provided a remote center compliance system having a variable center having an upper plate and a lower plate, and a plurality of elastic bodies installed between the upper and lower plates, the system comprising a plurality of lower rotary plates, each having a rotation axis parallel to a center axis passing the center of the lower plate and the center of the upper plate, and coupled to a lower end of each of the elastic bodies and coupled to the lower plate to be capable of rotating, and a plurality of upper rotary plates, each being coupled to an upper end of each of the elastic bodies and concurrently coupled to the upper plate to be capable of rotating about the rotation axis of the lower rotary plate, in which a center axis of each of the elastic bodies is inclined with respect to the rotation axis of the lower rotary plate to which each of the elastic bodies is coupled.
It is preferred in the present invention that the system further comprises a lower rotary plate position fixing means for preventing rotation of the lower rotary plates and an upper rotary plate position fixing means for preventing rotation of the upper plates.
Also, it is preferred in the present invention that the lower rotary plate position fixing means comprises a plurality of lower position determination holes formed along the outer circumferential surface of each of the lower rotary plates, and a lower position fixture installed at the lower plate to be capable of advancing or retreating with respect to the outer circumferential surface of each of the lower rotary plates so that the lower position fixture can be inserted in one of the lower position determination holes when the lower position fixture advances to the outer circumferential surface of each of the lower rotary plates, and the upper rotary plate position fixing means comprises a plurality of upper position determination holes formed along the outer circumferential surface of each of the upper rotary plates, and a upper position fixture installed at the upper plate to be capable of advancing or retreating with respect to the outer circumferential surface of each of the upper rotary plates so that the upper position fixture can be inserted in one of the upper position determination holes when the upper position fixture advances to the outer circumferential surface of each of the upper rotary plates.